A review of the current science of intermittent fasting suggests its potential for weight-loss and the reversal of a range of medical conditions.
In a review article published in The New England Journal of Medicine, John Hopkins medicine neuroscientist (Mark Mattson, Ph.D.) reviews the current science of intermittent fasting. Findings suggest it can help with weight-loss and reversing obesity, diabetes, cardiovascular disease, cancers, and neurodegenerative brain diseases without the use of synthetic drugs.
What is intermittent fasting?
Intermittent fasting, or cycling between periods of eating and longer periods of not eating, may seem daunting in the modern era where a typical day includes three meals plus snacks. Commonly studied intermittent fasting regimens include alternate-day fasting, 5:2 (fasting two days each week), and daily time-restricted eating (for example fasting 16 to 18 hours a day).  For some, it may be challenging to adopt an intermittent-fasting lifestyle because of the cultural expectation to eat and the constant exposure to food marketing aiming to lure us with delicious foods. Initial side-effects of intermittent fasting may include hunger, irritability, and a lower ability to focus, with side effects generally disappearing within the first month.
Intermittent fasting induces a metabolic switch
It is thought that fasting induces a metabolic switch from the use of liver-derived glucose as the primary energy source to the use of fat from adipose tissue as the form of energy production. During fasting, fat is broken down into fatty acids and glycerol and the liver converts these fatty acids into ketone bodies. Ketone bodies are metabolized to generate energy for cells and they are involved in signaling activities that activate adaptive cellular pathways that promote survival. An organism’s innate defense system against oxidative stress and ability to remove or repair damaged molecules may be enhanced as a result of these activated pathways. Synthesis, growth, and reproduction are also minimized to conserve energy.  The specific mechanisms at play are yet to be fully understood.
The health benefits of intermittent fasting
Mattson asserts that periodic metabolic switching improves blood sugar regulation, stress resistance, and inflammation, all indicators of good health. It can also affect cardiovascular health, including blood pressure, blood lipid levels, and resting heart rates in humans and animals. Unfortunately, people who overeat or who eat several times a day do not experience the benefits of this metabolic switch.
Mounting evidence suggests that intermittent fasting is effective for preventing obesity in animals and adults, in addition to, reversing insulin resistance in patients with prediabetes or type 2 diabetes as shown in two recent studies. Another study demonstrated that 100 overweight women who were on the 5:2 intermittent fasting regimen had greater insulin sensitivity and less belly fat than women who lost the same amount of weight in a calorie-reduction group.
Numerous studies in animals have shown that alternate-day fasting reduces the occurrence of spontaneous tumors in rodents and suppresses the growth of induced tumors. More research is required to see if humans are affected the same way and clinical trials are in progress. Already there are some glioblastoma (brain tumor) case studies suggesting that intermittent fasting can suppress tumor growth. It is not yet clear whether fasting affects cancer recurrence in people.
Preclinical studies of alternate-day fasting in animals have found a delay in the onset and progression of Alzheimer’s disease and Parkinson’s disease. Preliminary findings have also shown that intermittent fasting may help alleviate asthma (in obese patients), multiple sclerosis (in mice and humans), rheumatoid arthritis symptoms (in adults) and improve tissue damage and surgical outcomes (in animals).
Recently, preliminary studies suggest that intermittent fasting can benefit multiple domains of cognitive performance or brain health, including working memory in both animals and adults. More studies are needed to prove the effects of intermittent-fasting on learning and memory, especially on older people and neurodegenerative diseases.
The article acknowledges that the long-term effects of intermittent fasting have yet to be determined and findings cannot be generalized beyond the studies included in the review.
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Written by Maria-Elena Bernal
References:
Effects of Intermittent Fasting on Health, Aging, and Disease | NEJM. (2020). Retrieved 4 January 2020, from https://www.nejm.org/doi/full/10.1056/NEJMra1905136
Hopkins Medicine. (n.d.). Intermittent fasting: live ‘fast,’ live longer? Retrieved from https://www.eurekalert.org/pub_releases/2019-12/jhm-ifl121819.php.
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